ASPIRE Spring 09 - Aspire - The Concrete Bridge Magazine

Longitudinal view of Bridge 22 on
Road 431 in Israel, built in precast
segmental cantilever construction.
Photo: Finley Engineering Group Inc.
Aerial view of the Ein Ha’kore Interchange of Road 431. Precast concrete segmental
bridges offer insights into how durability and sustainable construction intertwine.
Photo: Danya-Cebus.
Road 431 in Israel
The introduction of external posttensioning
tendons has also helped
change the nature of the corrosion
protection system, as illustrated by the
Road 431 project in Israel.
Time was the most compelling reason
to use precast segmental construction
with external tendons on the Road
431 Ein Ha’kore Interchange Bridges in
Israel. With a very limited design and
construction schedule, and several other
aspects of the overall roadway project
dependent on prompt completion of the
interchanges, the project team needed
to perform quickly.
Deviation segment featuring posttensioning
tendon diabolos in the
foreground. Photo: Finley Engineering
Group Inc.
The external post-tensioning system
reduced the segment cross-sectional
area, including narrower web width
and bottom slab thickness. This resulted
in lower superstructure weight and
foundation loads, and better utilization
and effectiveness of the post-tensioning
system. With smaller sections, the same
post-tensioning force achieved higher
compressive stress in the concrete and
reduced cracking potential, meaning
lower cost and better performance.
Also, external tendons meant that fewer
segments required post-tensioning
embedments and associated details, so
segment casting was faster and more
efficient. The system reduced posttensioning
operations in the field as
there were fewer tendons to install,
less anchorage hardware, and fewer
stressing operations. The continuous
duct also reduced the number of
connections.
When considered collectively, these
factors positioned the Road 431 project
as a model of sustainability.
Because Road 431 is a build-operatetransfer
project, contractor/concessionaire
Danya-Cebus was particularly sensitive
to durability issues and conscious of
inspection and maintenance of the
infrastructure. Since it is a toll road, any
shutdown for inspection or maintenance
would reduce income. So staying out
was equally as important as getting in
and getting out.
Because external tendons are not
encased in concrete, maintenance
teams can ensure that all strands remain
protected against harmful exposures
by simple visual inspection of the
tendon ducts. External tendons can be
inspected for nearly their entire length
and repair teams can repair any defect
from inside the box girder. Such defects
would include grout voids, split ducts,
and tendon damage.
Conclusion
By focusing on getting in, getting
out, and staying out, a bridge design
and construction team can contribute
greatly to sustainability goals. Less
construction time usually means fewer
traffic problems and, as a result, reduced
smog, faster commute times, and an
overall improvement in qualify of life. A
more durable bridge means less down
time for inspection and maintenance,
a higher level of safety, and a longerlasting
structure.
In the United States, with billions of
dollars from the stimulus bill likely to
be spent on bridge construction and
reconstruction, and an industry wisely
focused on increasing sustainability in
all areas, we should continue our quest
for innovation and improvement in our
construction processes and techniques.
This way, our country’s investment in
bridge infrastructure will be rewarded
with highly efficient, rapidly built, and
low-maintenance structures that do their
job and do it for a long, long time.
For more information on this or other
projects, visit www.aspirebridge.org.
16 | ASPIRE, Spring 2009